We report a case of renal metastases from prostate cancer to show that the possibility of tumor metastasis, although rare, should be considered in the differential diagnosis of renal mass. A 67-year-old man was found to have a renal mass on computed tomographic scan incidentally. He had had total androgen blockage (bicalutamide + leuprolerin) and chemotherapy (docetaxel hydrate ) for treatment of prostate cancer discovered 33 months ago. On the basis of the clinical features and radiologic results, the patient was thought to have a second malignant tumor, and we performed left nephrectomy. The pathological finding of this case was renal metastasis from prostatic adenocarcinoma. He died 18 months postnephrectomy.